The system of this application is designed to control the attitude of a satellite. Satellites must be maintained in a predetermined orbit and attitude in order to accomplish the assigned mission which can be surveillance, photography, detection and many others. The orbit and attitude of the satellite must be periodically adjusted to compensate for disturbances which occur in space or for the purpose of changing the mission.
In general, space craft attitude is adjusted by activating actuators, such as, momentum wheels, magnetic torguers, or thrusters in response to an attitude correction signal. The attitude error may be sensed by reference to sensors monitoring the position of the sun, stars and earth relative to the satellite or by onboard inertial sensors such as gyroscopes. The attitude is adjusted to its mission orientation in which the imaging system is pointed at its predetermined target and is maintained in this orientation during orbital flight. During flight the satellite is subject to motions induced by external forces, on board mechanisms or other sources and the attitude control system must continuously monitor and adjust attitude. Attitude control is therefore of primary importance in order to point the satellite to accomplish its mission and to maintain that position with the required accuracy.
It is the purpose of this invention to simplify attitude control and construct a less expensive system by eliminating some of the more expensive processes and components. The system of this invention eliminates the need for reliance on earth sensing and inertial sensing, thereby elliminating an earth sensing system and a gyroscope based inertial sensing system.